[committed] libstdc++: Fix std::format output of %C for negative years
Checks
Commit Message
Tested x86_64-linux. Pushed to trunk.
-- >8--
During discussion of LWG 4022 I noticed that we do not correctly
implement floored division for the century. We were just truncating
towards zero, rather than applying the floor function. For negative
values that rounds the wrong way.
libstdc++-v3/ChangeLog:
* include/bits/chrono_io.h (__formatter_chrono::_M_C_y_Y): Fix
rounding for negative centuries.
* testsuite/std/time/year/io.cc: Check %C for negative years.
---
libstdc++-v3/include/bits/chrono_io.h | 9 +++++++--
libstdc++-v3/testsuite/std/time/year/io.cc | 7 +++++--
2 files changed, 12 insertions(+), 4 deletions(-)
@@ -820,9 +820,14 @@ namespace __format
if (__conv == 'Y' || __conv == 'C')
{
- if (__is_neg)
- __s.assign(1, _S_plus_minus[1]);
int __ci = __yi / 100;
+ if (__is_neg) [[unlikely]]
+ {
+ __s.assign(1, _S_plus_minus[1]);
+ // For floored division -123//100 is -2 and -100//100 is -1
+ if ((__ci * 100) != __yi)
+ ++__ci;
+ }
if (__ci >= 100) [[unlikely]]
{
__s += std::format(_S_empty_spec, __ci / 100);
@@ -43,8 +43,11 @@ test_format()
s = std::format("{}", --year::min()); // formatted via ostream
VERIFY( s == "-32768 is not a valid year" );
- s = std::format("{:%y} {:%y}", 1976y, -1976y);
- VERIFY( s == "76 76" ); // LWG 3831
+ s = std::format("{:%C %y} {:%C %y}", 1976y, -1976y);
+ VERIFY( s == "19 76 -20 76" ); // LWG 3831
+
+ s = std::format("{:%C %y} {:%C %y} {:%C %y}", -9y, -900y, -555y);
+ VERIFY( s == "-01 09 -09 00 -06 55" ); // LWG 4022
s = std::format("{0:%EC}{0:%Ey} = {0:%EY}", 1642y);
VERIFY( s == "1642 = 1642" );